Most Americans cannot afford to spend big on Transatlantic vacations. So the loud people are most often people in a certain income bracket & higher who are just mannerless in the first place. These are also the people who get pissed off that (insert country here) is not speaking English to them.
America has a reputation, and not just as vacationers, for doing everything over the top and at high volume. Just listen to people when you are out.
[runs screaming from the room]